Particulate arresting means for cyclonic separator

ABSTRACT

A gas stream containing suspended particulate material is blown tangentially into the body of a cyclonic separator and swirls around the body in a cyclonic path. An exhaust conduit at the upper end is surrounded by a larger sleeve to provide an annular space around the exhaust conduit which is large enough to admit a swirling ring of a gas containing suspended particulate material. An opening is formed in the sleeve for tangentially skimming gas and particulate material from the annular space and a damper is adjustably mounted adjacent to the opening for controlling the flow of gas and particulate material therethrough. When used to recycle exhaust gases to a dryer furnace the damper is adjusted to return an amount of air which meets the requirements of the dryer.

United States Patent Lindl Apr. 2, 1974 [75] Inventor: Gordon J. Lindl, Milwaukee, Wis.

[73] Assignee: Arnold Dryer Company, Milwaukee,

Wis.

[22] Filed: Oct. 10, 1972 [21] Appl. No.: 296,429

[52] US. Cl. 34/79, 34/57 E [51] Int. Cl. F26b 21/06 [58] Field of Search 34/79, 102, 57 R, 57 E;

[56] References Cited UNITED STATES PATENTS 2,414,641 1/1947 French 55/338 2,143,505 H1939 3,396,681 8/1968 3,749,382 7/1973 3,526,483 9/1970 Deussner et a1. 55/340 Primary ExaminerJohn J. Camby Assistant Examiner-James C. Yeung Attorney, Agent, or FirmArthur L. Morsell, Jr.

[57] ABSTRACT A gas stream containing suspended particulate material is blown tangentially into the body of a cyclonic separator and swirls around the body in a cyclonic path. An exhaust conduit at the upper end is surrounded by a larger sleeve to provide an annular space around the exhaust conduit which is large enough to admit a swirling ring of a gas containing suspended particulate material. An opening is formed in the sleeve for tangentially skimming gas and particulate material from the annular space and a damper is adjustably mounted adjacent to the opening for controlling the flow of gas and particulate material therethrough. When used to recycle exhaust gases to a dryer furnace the damper is adjusted to return an amount of air which meets the requirements of the dryer.

1 Claim, 3 Drawing Figures TO BURNER CONTROL Pmmmm 2 m4 3300.429

F :9 -1 I I 56 mum 44 To ER CONTROL BACKGROUND OF THE INVENTION This invention relates to cyclonic separators for separating suspended particulate matter from a gas stream in which the particulate material is suspended. Such cyclonic separators usually have a cylindrical body into which the gas stream is tangentially blown or drawn so that it swirls around the body in a cyclonic path. The body has a downwardly tapered bottom chamber and a top exhaust conduit, Most of the particulate material in the swirling gas stream is thrown outwardly away from the exhaust conduit and drops due to the force of gravity into the bottom chamber of the separator and from there through an opening into a suitable receptacle therebelow. The remaining gas and light particulate matter is drawn away through the exhaust conduit in the top.

Such cyclonic separators have been used successfully for many years in numerous applications, but in recent years, increasingly strict air pollution standards have made it necessary to reduce the amount of light particulate material in the exhaust from such separators. Accordingly, the principal object of this invention is to provide particulate arresting means for removing light particulate material from the exhaust of cyclonic separators.

Another object of this invention is to provide particula te arresting means of the above-noted character which is simple and sturdy in structure.

A further object of the invention is to provide in combination with a dryer furnace, means for recycling exhaust gases to said furnace, and novel means for regulating the amount of gases which are recycled to suit the requirement of the dryer, said requirement varying inversely with the amount of water being evaporated in the dryer.

A further object of this invention is to provide particulate arresting means of the above-noted character which is relatively inexpensive in cost.

SUMMARY OF THE INVENTION In accordance with this invention, the above-noted objects are attained by providing a sleeve which surrounds the exhaust conduit of a cyclonic separator and forms a surrounding space around the lower end of the conduit. The surrounding space is large enough to admit a swirling ring of gas containing suspended particulate material. An opening is formed in the sleeve for tangentially skimming gas and particulate material from the annular space and a damper is adjustably mounted in the annular space adjacent to the opening for controlling the flow of gas and particulate material therethrough.

DESCRIPTION OF THE DRAWINGS FIG. 1 is a plan view of one illustrative embodiment of the invention as used in connection with a dehydrator system for hay, alfalfa, or the like;

FIG. 2 is an enlarged axial sectional view through the separator of the embodiment shown in FIG. 1; and

I FIG. 3 is a cross section taken on the line 33 of FIG. 2.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to FIG. 1, one illustrative embodiment of the invention is utilized in connection with a dehydrator system including a furnace having an outer wall 12, an inner wall 14, and an annular air space 16 between the two walls. Furnace 10 is supported on a base 18. A burner 20 is mounted at one end of the furnace and primary combustion air is supplied to the burner 20 through an air inlet duct 22 from a blower 24. The inlet air for blower 24 may be drawn through the annular air space 16 in furnace 10 by way of conduit 26. The inlet air drawn through annular air space 16 is preheated by the furnace 10 and provides a useful outlet for heat which would otherwise be wasted as radiation from the walls of the furnace. Suitable air inlet openings are provided in the outer wall 12 of furnace 10 to admit fresh air into air space 16 as indicated by the arrow (a) in FIG. 1.

The outlet end of furnace 10 is coupled by means of a duct 28 to the inlet end of a rotary drum dryer 30. The duct 28 has a feed duct 32 coupled thereto for receiving the wet product to be dried. This may be hay, alfalfa, brewers grains, or any other suitable material. The ducts 28 and 32 are coupled together by well known prior art means which includes an air seal for preventing cold air from being drawn into dryer from feed duct 32.

A fan 34 is coupled to the outlet of the rotary drum dryer 30 by means of an outlet duct 36. The fan 34 is driven by an electric motor 38 which, in its simplest form, operates at a constant speed to provide a constant volume delivery.

In the preferred embodiment of the invention, the speed of electric motor 38 is controlled via a control circuit 40 in accordance with the amount of moisture present in the wet product input. This is determined by a moisture sensor 42 which is mounted in the feed duct 32. The moisture sensor 42 continuously senses the relative amount of moisture in the product being inserted into the feed duct 32 and develops an electrical output signal which is proportional to the amount of moisture in the product. This electrical signal is applied to the control circuit 40 which speeds up the motor 38 when the moisture content in the product increases and slows the motor down when the moisture content in the product decreases.

The wet product introduced into rotary drum dryer 30 through feed duct 32 is tumbled in the dryer and moved therethrough from left to right in the drawing by suitable flights in the dryer. Hot gases from furnace 10 are blown across the wet product while it is passing through the dryer 30 to evaporate the moisture therefrom before the product reaches the outlet duct 36. The hot gas stream through rotary drum dryer 30 is a result of the combined effect of fan 34 and furnace blower 24. The temperature of the hot gas stream in outlet duct 36 may be sensed by a thermostat 44 which is electrically coupled to suitable means for varying the heat output of burner 20 of furnace 10 to maintain a constant temperature output at the outlet duct 36.

The dried product and hot gases emerging from outlet duct 36 are blown by fan 34 through a duct 48 into a centrifugal cyclonic separator 50. The dried product and hot gases that pass through duct 48 are introduced tangentially into the section 52 of separator 50, where they swirl around in a cyclone-shaped path which tends to move the dried product and the heavy particulate material outwardly under the influence of centrifugal force. A downwardly-tapering bottom section 54 having an open bottom is attached to the bottom of section 52. The dried product and heavy particulate material swirl around the inner wall of bottom section 54, being drawn downward by the force of gravity until they drop out the open bottom of bottom section 54 and into a suitable storage receptacle thereunder. The hot gases and lighter particulate material are discharged out of an exhaust conduit assembly at the top of section 52 as will be described below.

Although most of the dried product and particulate material fall out of the bottom of separator 50, a certain amount of the lighter particulate material stays with the exhaust gases. in the present invention, additional particulate arresting means is provided at the top of separator 50 to separate out most of the lighter particulate matter from the exhaust gases. In the prior art separators, the exhaust means consisted of an exhaust conduit which was attached to the upper end of section 52 with a damper such as the damper 58 adjustably mounted within the exhaust conduit. In my copending application, Ser. No. 246,530, a portion of the exhaust gases is recycled back to the furnace through the burner to incinerate the particulate material therein. With the structure of said prior application it was found, by experiment, that only 35 percent of the total particulate material going to atmosphere could be removed while a minimum of 60 percent can be removed with the apparatus of the present invention.

Referring to FIGS. 2 and 3, the apparatus of this invention includes a sleeve 60 which is attached within a collar 62 at the upper end of the section 52. The upper portion of sleeve 60 surrounds the lower end of exhaust conduit 56 to form an annular space 64 therearound. Sleeve 60 is flanged inwardly at its top as at 66 with said flange attached at its inner periphery around exhaust conduit 56. Sleeve 60 extends downwardly as at 68 below the lower end of exhaust conduit 56 and also below inlet duct 48 to form a chamber 69 for receiving inflow from inlet duct 48. Although, in the preferred embodiment, sleeve 60 is coaxial with exhaust conduit 56, it should be understood that sleeve 60 may be eccentric with respect to exhaust conduit 56 to form an involute or scroll patem for the cross-sectional shape of annular space 64.

The difference between the cross-sectional dimensions of exhaust conduit 56 and sleeve 60 is selected to define an annular space 64 which is large enough in radial dimension to admit a swirling ring of gas containing suspended solid particles. This ring of swirling gas and suspended particles is skimmed off through an opening 70 which is formed in sleeve 60. A tangential outlet duct 72 is attached to sleeve 60 around opening 70. In this embodiment of the invention, the outlet duct 72 is coupled to a feedback conduit 74 which recycles the able closure for opening 70. The free edge of damper 78 projects into the swirling effluent stream in annular space 64 to act as a skimmer for the swirling effluent.

In the operation of this embodiment, the dried product and hot gases from dryer 30 are blown tangentially through duct 48 into the section 52 of cyclonic separator 50. The section 52 is circular in its cross-sectional shape and thereby causes the dried product and hot gases to swirl around the interior of section 52 along a cyclonic path which moves the dried product and heavier particulate matter outwardly under the influence of centrifugal force. This heavier material swirls around in the space between the wall of section 52 and the lower portion 68 of sleeve 60 and gradually settles downward into bottom section 54 under the influence of gravity. The fact that the lower portion 68 of sleeve 60 extends below tangential inlet duct 48 minimizes the amount of particulate matter which is drawn upwardly with the hot exhaust gases flowing upwardly through sleeve 60 and exhaust conduit 56. In spite of this, however, a portion of the lighter particulate matter is drawn upwardly, but most of it is in the outer layers of the gas column due to its swirling motion. At least 60% of this light particulate matter is trapped in the annular space 64, which is closed at the top, and said matter is recycled through opening and ducts 72 and 74 back to the burner 20 of furnace 10 where the particulate matter is incinerated. This substantially reduces the particulate matter in the exhaust gases which are discharged from exhaust stack 56.

In the operation of this embodiment, the damper 78 is adjusted manually via handle 80 to recycle the desired amount of skimmed effluent back to the air intake for burner 20. If the dryer is operating at its peak evaporation ability, the damper 78 will normally have to be turned in a direction to restrict the opening 70 because the air input requirements of the dryer vary inversely with the amount of water being evaporated in the dryer. At lower water evaporation levels, the damper 78 can be turned in the direction to enlarge the opening 70. For any given application of the dryer system, the damper 78 is preferably opened as far as conditions permit for maximum recirculation of the skimmed effluent, which coincides with maximum reduction of the particulate material in the exhaust output from cyclone separator 50.

Although the effluent skimmed off from annular space 64 is recycled and incinerated in this particular embodiment of the invention, it should be understood that other arrangements are possible, e.g. the skimmed effluent may be led to a point downstream of the burner, may be led away to a separate furnace, to another cyclonic separator, to a dust room, to a water scrubber, or to any other suitable device for disposing of the unwanted particulate material. Also, it will be understood that automatic controls may be added if desired to automatically control the setting of damper 78 in accordance with the air input requirements of the dryer. Other modifications of the disclosed structure will be apparent to those skilled in the art, and it should be understood that this invention includes all modifications which fall within the scope of the following claims.

What I claim is:

1. In combination, a dryer having an inlet and an outlet, a furnace having a burner and having an air inlet for admitting air to said burner and having a hot gas outlet for exhausting heated gases from said furnace, the hot gas outlet of the furnace being coupled to the inlet of said dryer, means for introducing a product to be dried into the inlet of said dryer, a centrifugal cyclonic separator having a hollow body and having inlet means connected to the outlet of said dryer, said body having an exhaust conduit, an enlarged sleeve secured to said body member and having a portion surrounding said exhaust conduit to provide an annular chamber which is large enough to accommodate swirling gas containing suspended particles, and said sleeve having an outlet opening communicating with the outer periphery of said annular chamber, means connecting said outlet opening to the air inlet of said burner for recycling gas with suspended solid particles to said burner to be incinerated thereby, a damper for said opening of the sleeve adjustably mounted in said annular chamber of said opening and having a free edge projecting in a direction opposite to the direction of swirling movement of the gases and swingable toward and away from the wall of said sleeve to vary the distance between said wall and damper edge and control the percentage of swirling gas which is skimmed off whereby the amount of gas which is recycled may be regulated to suit the requirements of the dryer while permitting maximum recirculation of skimmed off gases. 

1. In combination, a dryer having an inlet and an outlet, a furnace having a burner and having an air inlet for admitting air to said burner and having a hot gas outlet for exhausting heated gases from said furnace, the hot gas outlet of the furnace being coupled to the inlet of said dryer, means for introducing a product to be dried into the inlet of said dryer, a centrifugal cyclonic separator having a hollow body and having inlet means connected to the outlet of said dryer, said body having an exhaust conduit, an enlarged sleeve secured to said body member and having a portion surrounding said exhaust conduit to provide an annular chamber which is large enough to accommodate swirling gas containing suspended particles, and said sleeve having an outlet opening communicating with the outer periphery of said annular chamber, means connecting said outlet opening to the air inlet of said burner for recycling gas with suspended solid particles to said burner to be incinerated thereby, a damper for said opening of the sleeve adjustably mounted in said annular chamber of said opening and having a free edge projecting in a direction opposite to the direction of swirling movement of the gases and swingable toward and away from the wall of said sleeve to vary the distance between said wall and damper edge and control the percentage of swirling gas which is skimmed off whereby the amount of gas which is recycled may be regulated to suit the requirements of the dryer while permitting maximum recirculation of sKimmed off gases. 